Inward-directed current generated by the Na+,K+ pump in Na+- and K+-free medium
✍ Scribed by Athina Efthymiadis; Jürgen Rettinger; Wolfgang Schwarz
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 445 KB
- Volume
- 17
- Category
- Article
- ISSN
- 1065-6995
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✦ Synopsis
Abstract
In Na^+^‐ and K^+^‐free solution, an inward‐directed current can be detected in Xenopus oocytes, which is inhibited by cardic glycosides and activated by ATP. Therefore, it is assumed to be generated by the Na^+^, K^+^ pump. At negative membrane potentials, the pump current increases with more negative potentials and with increasing [H^+^] in the external medium. This current is not observed when Mg^2+^ instead of Ba^2+^ is the only divalent cation present in the bath medium, and it does not depend on whether Na^+^ or K^+^ is present internally. At 5 to 10 mM Na^+^ externally, maximum pump‐generated current is obtained while no current can be detected in presence of physiological [Na^+^]. It is suggested that in low‐Na^+^ and K^+^‐free medium the Na^+^, K^+^ pump molecule can either form a conductive pathway that is permeable to Ba^2+^ or protons or operate in its conventional transport mode accepting Ba^2+^ as a K^+^ congener. A reversed pump mode or an electrogenic uncoupled Na^+^‐efflux mode is excluded.